JPH0446576A - Control circuit for rotational speed of motor - Google Patents

Abstract

PURPOSE:To prevent an excess over the dynamic range of a D/A conversion circuit and the impossibility of control by generating applied voltage and reducing an analog signal only by the section of applied voltage when the analog signal exceeds the set voltage or more of a load current detector when load as disturbance is applied to a motor. CONSTITUTION:When load as disturbance is applied to a motor 25, the number of revolution corresponding to the frequency of a reference speed signal 1 intends to be kept. The value of an analog signal 4 rises and intends to exceed the dynamic range of a D/A conversion circuit 22, but applied voltage 5 is generated before the value of the analog signal 4 exceeds the dynamic range of the D/A conversion circuit 22 by previously bringing the set voltage 8 of a load current detector 27 to a value slightly smaller than the value of a current conversion voltage 7 at a time when the value of the analog signal 4 exceeds the dynamic range of the D/A conversion circuit 22, and applied voltage 5 is applied to the analog signal 4 in a summing amplifier 23. The analog signal 4 is reduced only by the application of applied voltage 5. Excess over of the dynamic range of the D/A conversion circuit 22 of the analog signal 4 and the impossibility of control can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor rotational speed control circuit, and particularly to a rotational speed control circuit used in a spindle motor drive circuit of a magnetic disk device.

[Conventional technology]

A conventional motor rotational speed control circuit used in a spindle motor drive circuit of a magnetic disk drive employs a circuit as shown in FIG.

That is, a rotation speed detection signal 10 indicating the actual rotation speed of the motor 35 to be controlled and a reference speed signal 9 indicating the target rotation speed of the motor 35 are input, and the difference in their frequencies is output as a digital signal 11. Speed error detection circuit 3
1, a digital-to-analog conversion circuit (D/A conversion circuit) 32 that inputs the digital signal 11, converts it to an analog signal 12, and outputs it, and inputs the analog signal 12 and supplies a current proportional to the voltage to the motor 35. It also includes a power amplifier circuit 34 for supplying power.

In the motor rotation speed control circuit configured in this way, since the motor is not rotating at the start of motor drive, the frequency difference between the rotation speed detection signal 10 and the reference speed signal 9 is extremely large, and the digital signal 11 is The value will be the highest value.

Therefore, the current converted by the D/A conversion circuit 32 and supplied from the power amplifier circuit 34 to the motor 35 also becomes a large value, and the motor 35 rotates vigorously and quickly reaches the speed corresponding to the frequency of the reference speed signal 9. Trying to become a number. When the rotation of the motor 35 reaches a rotation speed corresponding to the frequency of the reference speed signal 9, it becomes a steady rotation, and thereafter it is controlled to maintain the steady rotation.

[Problem to be solved by the invention]

In the conventional motor rotation speed control circuit as described above, in order to control the rotation of the motor with high precision, the resolution of the rotation speed control range, that is, the resolution of the D/A conversion circuit must be improved. , D , / Increase the resolution by increasing the number of bits of the A conversion circuit, or
Analog signal 1 across the dynamic range of the conversion circuit
Either the voltage value per bit of 2 must be reduced.

However, in the former case, it is difficult to realize because the cost is high, so the latter is an effective method, but if the dynamic range of the D/A conversion circuit is narrowed, When the rotational speed control range is limited and a load as a disturbance is applied to the motor, the rotational speed control circuit, which forms a feedback loop, attempts to maintain the rotational speed corresponding to the frequency of the reference speed signal 9. . Therefore, the value of the analog signal 12 increases and exceeds the controllable range, resulting in a drawback that control becomes impossible.

[Means to solve the problem]

The motor rotation speed control circuit of the present invention inputs a rotation speed detection signal indicating the actual rotation speed of the motor to be controlled and a reference speed signal indicating the target rotation speed of the motor, and calculates the difference in their frequencies. A speed error detection circuit that outputs as a digital signal, a digital-to-analog conversion circuit that inputs the digital signal, converts it to an analog signal, and outputs it, and inputs the motor current and outputs a current-converted voltage corresponding to the value. a current-voltage conversion circuit that inputs the current conversion voltage and a set voltage of a constant value, compares them, and outputs an applied voltage of a constant value when the current conversion voltage is greater than the set voltage. a current detection circuit; a summing amplifier that inputs the output signal of the digital-to-analog conversion circuit and the applied voltage and outputs a signal obtained by adding them; and a summing amplifier that inputs the output signal of the summing amplifier and outputs a signal proportional to the voltage. and a power amplifier circuit that supplies current to the motor.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, a speed error detection circuit 21 receives a rotation speed detection signal 2 indicating the actual rotation speed of a motor 25 to be controlled.
and a reference speed signal 1 indicating the target rotational speed of the motor 25 are input, and the difference in their frequencies is output as a digital signal 3. The D/A conversion circuit 22 receives the digital signal 3, converts it into an analog signal 4, and outputs the analog signal 4. The current-voltage conversion circuit 26 inputs the current value 6 of the motor 25 and outputs a voltage (current conversion voltage) 7 corresponding to the current value.

The load current detection circuit 27 inputs the current conversion voltage 7 outputted from the current-voltage conversion circuit 26 and the set voltage 8 of a constant value, compares them, and only when the current conversion voltage 7 is larger than the set voltage 8 An applied voltage of a predetermined value is output. The summing amplifier 23 inputs the analog signal 4 output from the D/A conversion circuit 22 and the applied voltage 5, and outputs a signal obtained by adding them. The power amplifier circuit 24 inputs the output signal of the summing amplifier 23 and supplies a current proportional to the voltage to the motor 25.

In the motor rotation speed control circuit configured in this way, since the motor is not rotating when the motor starts driving, the frequency difference between the rotation speed detection signal 2 and the reference speed signal 1 is extremely large, and the digital signal 3 is The value will be the highest value. Therefore, the current converted by the D/A conversion circuit 22 and supplied from the power amplifier circuit 24 to the motor 25 also becomes a large value, and the motor 25 rotates vigorously. When a large current flows through the motor 25, the current conversion voltage 7 from the current-voltage conversion circuit 26 becomes larger than the set voltage 8, and the load current detection circuit 27 operates to output the applied voltage 5 to the summing amplifier 23. Since the summing amplifier 23 inputs the analog signal 4 and the applied voltage 5 and outputs a signal obtained by adding them to the power amplifier circuit 24, the rotation of the motor 25 is quickly adjusted to the reference speed by the amount of the applied voltage 5. A steady rotation defined by signal 1 can be reached.

After the rotation of the motor 25 reaches steady rotation, when a load as a disturbance is applied to the motor 25, the rotation speed corresponds to the frequency of the reference speed signal 1 because the rotation speed control circuit forms a feedback loop. Therefore, the value of the analog signal 4 increases and tries to exceed the dynamic range of the D/A conversion circuit 22, but the set voltage 8 of the load current detection circuit 27 is
By setting the current conversion voltage 7 to a value slightly smaller than the value of the current conversion voltage 7 when exceeding the dynamic range of added to. Therefore, the analog signal 4 decreases by the amount of the applied voltage 5, and it is possible to prevent the dynamic range of the D/A conversion circuit 22 from being exceeded and control becoming impossible3. [Effect of the invention] As explained above, in the motor rotation speed control circuit of the present invention, when the motor starts driving, the current supplied to the motor becomes a large value, and the current conversion voltage from the current conversion circuit becomes larger than the set voltage. Since an applied voltage is generated, there is an effect that the rotation of the motor can reach steady rotation more quickly than before by the amount of applied voltage.

In addition, after the motor rotation reaches steady rotation, when a load as a disturbance is applied to the motor, an applied voltage is generated when the voltage exceeds the set voltage of the load current detection circuit, and the analog signal decreases by that amount. This has the effect of preventing control from becoming impossible due to exceeding the dynamic range of the [)7/Δ conversion circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a conventional motor rotation speed control circuit. 21・31... Speed error detection circuit, 22・32
......D,/A conversion circuit, 23...-
Summing amplifier, 24/34... Power amplifier circuit, 25/35... Motor, 6... Current voltage conversion circuit, 7... Load current detection circuit .

Claims (1)

[Claims] 1. A rotation speed detection signal indicating the actual rotation speed of the motor to be controlled and a reference speed signal indicating the target rotation speed of the motor are input, and the difference in their frequencies is converted into a digital signal. A speed error detection circuit that outputs a speed error detection circuit, a digital-to-analog conversion circuit that inputs the digital signal, converts it to an analog signal, and outputs it, and a current voltage that inputs the motor current and outputs a current-converted voltage corresponding to the value. a conversion circuit;
a load current detection circuit that inputs the current conversion voltage and a set voltage of a constant value, compares them, and outputs an applied voltage of a constant value when the current conversion voltage is larger than the set voltage; a summing amplifier that inputs the output signal of the analog conversion circuit and the applied voltage and outputs a signal obtained by adding them; and a summing amplifier that inputs the output signal of the summing amplifier and supplies a current proportional to the voltage to the motor. A motor rotation speed control circuit comprising a power amplifier circuit. 2. A speed error detection circuit that inputs a rotation speed detection signal indicating the actual rotation speed of the motor to be controlled and a reference speed signal indicating the target rotation speed of the motor, and outputs the difference in their frequencies as a digital signal. a digital-to-analog conversion circuit that inputs the digital signal, converts it to an analog signal, and outputs it; a current-voltage conversion circuit that inputs the motor current and outputs a current-converted voltage corresponding to the value;
a load current detection circuit that inputs the current conversion voltage and a set voltage of a constant value, compares them, and outputs an applied voltage of a constant value when the current conversion voltage is larger than the set voltage; a summing amplifier that inputs the output signal of the analog conversion circuit and the applied voltage and outputs a signal obtained by adding them; and a summing amplifier that inputs the output signal of the summing amplifier and supplies a current proportional to the voltage to the motor. a power-up circuit, and the set voltage is set to a value slightly smaller than the value of the current conversion voltage when the dynamic range of the digital-to-analog conversion circuit is exceeded.